The present invention relates to a semiconductor device including an antifuse as the memory device.
One type of memory device is the nonvolatile memory (OTP: One Time Programmable Device) which is incapable of being rewritten. The OTP device is typically known as a memory device type with an electrically conductive path (fuse) made from the same material as the gate electrode (e.g. polysilicon) or the same material as the wiring (e.g. copper or aluminum) and that breaks due to melting or electromigration.
In recent years, demands have been made for an OPT device whose internal written information is difficult to analyze. Memory device types containing a fuse that breaks or blows have the problem that methods such as image processing can easily analyze whether the fuse is broken so that the information written in the device can be analyzed, as for example described in Greg Uhlmann and others, “A Commercial Field-Programmable Dense eFUSE Array Memory with 99.999% Sense Yield for 45 nm SOI CMOS,” 2008 IEEE INTERNATIONAL SOLID-STATE CIRCUITS CONFERENCE, SESSION 22, 22.4.
Antifuse type memory devices are being developed as OTP devices in recent years. These antifuse type memory devices (see for example Japanese Patent No. 4410101 and Japanese Unexamined Patent Publication No. 2009-290189) write information by applying a voltage higher than the breakdown voltage to the insulator (dielectric) film such as the gate insulator film or MIM capacitor to destroy the insulation. Analysis such as by image processing is impossible in antifuse type memory devices whose gate insulator film was destroyed after setting the appropriate conditions for destroying the film.